The present invention relates to an apparatus for monitoring leakage into the exhaust gas line or path of an internal combustion engine having oxygen concentration sensing and signaling means such as a lambda probe in the path for controlling the ratio of the air/fuel mixture fed to the engine.
Lambda probes are conventionally located in the exhaust gas path of internal combustion engines to measure the oxygen concentration in the exhaust gas for accordingly determining by feedback technique the proper ratio of the air/fuel mixture to be fed to the engine. The output signal of the lambda probe has a step at an air/fuel mixture ratio of 1, so that the engine can be regulated to operate with an air/fuel ratio of about such value. In normal operation, the lambda probe output signal contains control oscillations of around 10 Hz, i.e. constituting the so-called lambda control frequency of the output signal.
By way of such lambda probe feedback technique, the formation of the air/fuel mixture fed to an engine intake valve can be controlled to achieve optimum combustion in the associated cylinder and optimum cleaning of the resulting exhaust gas in a conventional three way catalytic converter located in the exhaust gas path downstream from the associated exhaust valve.
A three way catalytic converter is normally used in the internal combustion engine exhaust line of a motor vehicle to make sure that the exhaust gas vented to the atmosphere meets governmental regulatory emission standards for hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NO.sub.x), e.g. in terms of maximum permitted emission concentrations (g/km or g/mi) of these three pollutants. This type catalytic converter typically uses a reducing catalyst to reduce nitrogen oxides in combination with an oxidation catalyst for overall three way emission control of hydrocarbons, carbon monoxide and nitrogen oxides.
It is only possible to achieve effective catalytic control of these three pollutants when the exhaust gas contains a very small amount of oxygen. This means that the ratio of the air/fuel mixture fed to the engine combustion chambers must be precisely controlled, with a view to maintaining it very close to an ideal stoichiometric combustion ratio. For this purpose, the exhaust gas composition is sensed and the carburetor or like device is adjusted in dependence on the composition via feedback control.
Since the exhaust gas is at a temperature too low for further reaction, treatment in a three way catalytic converter is necessary. However, an increased level of oxygen in the exhaust gas decreases the ability of the catalytic converter to treat the three stated pollutants in the desired manner. This adverse situation is aggravated when the exhaust gas path is subject to suction leakage of atmospheric pressure external air into the exhaust path as can occur during intermittent reduced pressure phases in the engine during operation. Generally, each combustion cycle of an internal combustion engine occurs several thousand times per minute, e.g. in an engine of the type used in gasoline fueled motor vehicles.
A requirement for the effectiveness of this arrangement is that the exhaust gas path be sealed against leakage, i.e. avoid any lack of proper sealing, as otherwise the exhaust gas cannot reach the three way catalytic converter in desired unchanged condition for proper catalytic cleaning before venting to the atmosphere. Internal combustion engine exhaust path sealing failures become evident particularly during reduced pressure phases in the engine operation, which are generated under certain operating conditions by a characteristic intermittent mode of internal combustion engine operation leading to pulsations. As a result of these pulsations, during a reduced pressure phase, comparatively high oxygen containing atmospheric pressure exterior air can penetrate into the engine exhaust gas path by suction leakage action at a sealing failure site.
It is desirable to provide means for detecting lack of sealing of the internal combustion engine's exhaust gas path, and particularly suction leakage of external air into such path.